1. Technical Field
Improved methods and downhole tools are disclosed for the imaging of a borehole for the purpose of properly orienting various downhole operational tools within the borehole. Improved logs in the form of rose-plots and cross-sectional images of boreholes are also disclosed.
2. Description of the Related Art
As the price of oil and gas increases and global supplies dwindle, oil and gas well completions are becoming more complex. Specifically, greater efforts are being expended at producing thinner, laminated reservoirs that may not have been produced in the past. Further, older, abandoned reservoirs are being reworked using enhanced oil recovery (EOR) and other techniques to extract as much remaining oil and gas as possible in contrast to past practices where such an older well may have been simply abandoned.
To meet the requirements of today's more complex completions, there is a growing need to survey or log and image the borehole and surrounding formation for the purpose of steering, positioning and orienting tools such as directional logging tools, re-entry tools, pipe cutters, whipstocks, directional flow meters, zero phase perforation guns, core samplers, fluid samplers, etc., in real-time. For example, FIGS. 1A-4 provide just some of the scenarios where a cross-sectional image of a borehole is needed.
Turning first to FIG. 1A, a borehole 10 is “open” or not-cased at the depth shown and includes two production strings or tubing strings 11, 12 that are resting against each other and are cemented in place in the borehole 10 in a decentralized position. A logging tool 13 has been lowered into the tubing 11. For this example, if the tubing 12 is producing adequately, it may be desirable, to perforate through the tubing 11 to the formation 14 without perforating or damaging the production tubing 12. Such a scenario would require proper orientation of a perforating gun lowered into the tubing 11 so that the charges are directed outward towards the formation 14 and away from the tubing 12 as well as away from the center of the borehole 10 which is filled with cement 15. Further, if there are problems associated with the production tubing 12, it may also be desirable to perforate the tubing 12 through the tubing 11 and produce reservoir fluid through the tubing 11 instead of the tubing 12.
The same borehole 10 at a different depth (or a different borehole) is shown in FIG. 1B where the tubing strings 11, 12 are spaced apart and more centered within the borehole 10. Again, it may be desirable to perforate the tubing 12 through the tubing 11 or direct charges towards the formation 14 from the tubing 11 and away from the tubing 12. In either scenario, a downhole image like those presented in FIGS. 1A-1B in real-time would be highly beneficial so that the perforation gun can be properly oriented.
A similar scenario is presented in FIGS. 2A-2B, wherein the section of borehole 10 shown is cased with an outer casing 16, which is cemented in place with the annular cement 17. It may be desirable to perforate the formation 14 through the tubing 11 and casing 16 without damaging the production tubing 12. Also, it may be desirable to perforate the production tubing 12 and produce through the tubing 11 in the event the production tubing 12 is damaged uphole or there are other problems associated with the production tubing 12 causing the well to be shut-in at the surface. On the other hand, it may be desirable to perforate the formation 14 without damaging the tubing 12.
In FIGS. 3A-3B, the borehole 10 is lined with casing 16 and cement 17. A production tubing string 12 and a logging tool 13 are shown. The logging tool 13 may have been lowered through a short production string (not shown at the depth illustrated in FIG. 3A) so that the logging tool 13 is disposed below the short production string or only a single production string 12 has been used as shown in FIG. 3B. Referring to FIG. 3A, proper orientation of the perforating gun is essential to avoid damage to the production tubing 12 and, referring to FIG. 3B, with the production string 12 in a decentralized position, proper orientation of the perforation gun is essential for exploiting the decentralized position of the tubing 12 against the casing 16 and formation 14.
Turning to FIG. 4, an uncased relief borehole 10a has been drilled in the vicinity of an older well or borehole 10. To utilize the borehole 10a as a relief well, perforations can be used to interconnect the boreholes 10, 10a. In such a situation, a borehole image, similar to the one shown in FIG. 4, is essential for properly orienting a perforation gun to ensure that shaped charges can traverse the formation 14a disposed between the boreholes 10a, 10.
In FIG. 5A, a borehole 10 is lined with casing 16 that is cemented in place as shown by the annular cement 17. A production tubing 12 is disposed within the casing 16b and includes a submersible pump cable 21 strapped to the outside diameter of the tubing 12 and held in place by a clamp assembly 22. If the borehole 10 is to be perforated, it is imperative that the perforating guns be directed away from the pump cable 21 and clamp assembly 22. Similarly, referring to FIG. 5B, the casing 16 may be equipped with a control cable or censor cable 23 that is held in place with a clamp assembly 22a. Obviously, perforation of the borehole 10 at the depth shown in FIG. 5B is must be carried out so that the sensor cable 23 is not damaged.
While all the above specific examples are directed primarily towards perforating, there is a need for improved techniques and tools for real-time borehole imaging and subsequent orientation of downhole operational tools and instruments including, but not limited to segment cutters, split-shots, chemical cutters, shot-sticks, reentry noses, punchers, core guns, whipstocks, directional flowmeters, pressure, temperature fluid samplers, and the like.
Thus, with today's complex well completions, there is a growing need for surveys and images of the borehole and immediate surroundings for the purpose of steering, positioning and orienting downhole operational tools in real-time. Such borehole imaging also has applications extending outside the oil & gas industry, such as surveying wells for river crossings or surveying subterranean tunnels or storage caverns.